1. Technical Field
The present disclosure relates to methods for forming an outer electrode of each of chip-type electronic components, and in particular, relates to methods for forming an outer electrode of each of electronic components in which electrode paste is applied to first end surfaces of a large number of electronic components that are held by a holding plate such that the first end surfaces of the electronic components protrude outward.
2. Background Art
In a well-known method for forming outer electrodes on both end surfaces of chip-type electronic components, a large number of electronic components are held by a holding plate such that first end surfaces of the electronic components protrude outward, and electrode paste is applied to the first end surfaces of the electronic components. After the electrode paste is dried, the holding position by the holding plate is changed such that the protruding end surfaces of the electronic components are reversed, and the electrode paste is similarly applied to second end surfaces of the electronic components. After the electrode paste is dried, the electronic components having the outer electrodes formed on both end surfaces are taken out of the holding plate.
Patent Document 1 proposes an electrode-applying apparatus including a collecting blade for scraping electrode paste on the bottom surface of a dip tank together to one side of the dip tank and a squeegee blade for adjusting the thickness of a paste film while leveling the electrode paste scraped together to the one side of the dip tank toward the other side. The collecting blade and the squeegee blade can be horizontally reciprocated in an integrated manner with respect to the dip tank.
Patent Document 2 proposes an apparatus for applying outer electrodes using a flat board and a box-shaped paste tank. The paste tank includes a side wall having a squeegee blade vertically slidable so as to adjust a gap from the flat board and the other side wall whose lower end portion is in close contact with the flat board. Furthermore, the paste tank stores electrode paste inside thereof. A paste film having a predetermined thickness can be spread on the flat board by sliding the paste tank along the flat board while a predetermined gap is maintained between the squeegee blade and the flat board. First end surfaces of electronic components held by a holding plate are dipped in the paste film spread on the flat board such that the electrode paste adheres to the first end surfaces of the electronic components. The electrode paste remaining on the flat board can be removed, i.e., collected, from the flat board by sliding the paste tank in a direction opposite to the direction of spreading the paste while the squeegee blade is in contact with the flat board.
When the electrode paste is applied to the end surfaces of the electronic components only one time, the film thickness values at corners of the electronic components tend to be small. Thus, the electrode paste is sometimes applied a plurality of times. According to the technologies described in Patent Documents 1 and 2, every time the paste film is spread and applied, the remaining paste needs to be collected (removed). Therefore, when the electrode paste is applied a plurality of times (herein, two times) as shown in FIG. 1, a tact time T is increased, and working efficiency is impaired.
The dip tank or the flat board can be extended to a length corresponding to that of a plurality of holding plates in the longitudinal direction such that the electrode paste being spread on this extended flat board is applied to the electronic components a plurality of times. In this method, the collection of the remaining paste is performed only one time after the electrode paste is applied a plurality of times, and thus the tact time can be reduced. However, in this method, there is a time difference between the first electrode application and the last electrode application after spreading the electrode paste, and the properties (such as viscosity) of the electrode paste are changed, during this period, due to volatilization of a solvent from the electrode paste spread as a thin film. In particular, when the electrode paste is spread so as to form a thin film, the surface area of the electrode paste is increased, and the volatilization of the solvent is accelerated. With this, application failures such as pinholes may occur in the paste applied to the electronic components.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 5-243109
Patent Document 2: Japanese Unexamined Patent Application Publication No. 7-161592